This invention relates to planetary transmissions and, more particularly, to a family of multi-speed planetary transmissions having three planetary gearsets.
Passenger vehicles include a powertrain that is comprised of an engine, multi-speed transmission, and a differential or final drive mechanism. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times as the transmission ratios are interchanged. The number of forward speed ratios that are available in a transmission determines the number of ratio interchanges that can occur and therefore the number of times the engine torque range can be repeated.
Early automatic transmissions had two speed ranges. This severely limited the overall speed range of the vehicle and therefore required a relatively large engine that could produce a wide speed and torque range. This resulted in the engine operating at a specific fuel consumption point, during cruising, other than the most efficient point. Therefore, manually shifted (countershaft transmissions) were the most popular.
With the advent of three and four speed automatic transmissions, the automatic shifting (planetary gear) transmission increased in popularity with the motoring public. These transmissions improve the operating performance and fuel economy of the vehicle. The increased number of speed ratios reduces the step size between ratios and therefore improves the shift quality of the transmission by making the ratio interchanges substantially imperceptible to the operator under normal vehicle acceleration.
It has been suggested that the number of forward speed ratios be increased to five and even six speeds. This has been accomplished in many heavy truck powertrains. Six speed transmissions are disclosed in U.S. Pat. No. 4,070,927 issued to Polak on Jan. 31, 1978; U.S. Pat. No. 5,106,352 issued to Lepelletier on Apr. 21, 1992; U.S. Pat. No. 5,542,889 issued to Pierce et al. on Aug. 6, 1996; U.S. Pat. No. 5,599,251 issued to Beim and McCarrick on Feb. 4, 1997; U.S. Pat. No. 6,071,208 issued to Koivunen on Jun. 6, 2000; U.S. Pat. No. 6,083,135 issued to Baldwin et al. on Jul. 4, 2000; and European Patent Application No. EP 1 033 510 A1 published Jun. 9, 2000.
Six speed transmissions offer several advantages over four and five speed transmissions, including improved vehicle acceleration and improved fuel economy. While many trucks employ six-speed transmissions, such as Polak, passenger cars are still manufactured, for the main part, with three and four speed automatic transmissions, and relatively few five or six speed devices due to the size and complexity of these transmissions. The Polak transmission provides six forward speed ratios with three planetary gearsets, two clutches, and three brakes. The Koivunen and Beim patents utilize six torque transmitting devices including four brakes and two clutches to establish the six forward speed ratios and one reverse ratio. The Lepelletier and the EP publications each employ three planetary gearsets, three clutches and two brakes to provide six forward speed ratios and one reverse ratio. One of the planetary gearsets in each of these publications is positioned and operated to establish two fixed speed input members for the remaining two planetary gearsets.
It is an object of this invention to provide an improved family of multi-speed transmissions having three planetary gearsets.
In one aspect of the present invention, each of the planetary gearsets has three members comprised of a sun gear member, a ring gear member, and a planet carrier assembly member.
In another aspect of the present invention, each of the planet carrier assembly members can be either of a single pinion or double pinion type planetary.
In still another aspect of the present invention, each transmission family member includes five torque-transmitting mechanisms comprised of three clutches and two brakes.
In yet another aspect of the present invention, the first member of the first planetary gearset is continuously interconnected with a first member of the second planetary gearset through an interconnecting member.
In a still another aspect of the present invention, the second member of the first planetary gearset is continuously interconnected with a first member of the third planetary gearset through a second interconnecting member.
In yet still another aspect of the present invention, the second member of the second planetary gearset is continuously interconnected with a second member of the third planetary gearset through a third interconnecting member.
In a further aspect of the present invention, a transmission input shaft is connected with at least one member of one of the planetary gearsets, and a transmission output shaft is continuously connected with another member of one of the planetary gearsets.
In yet a further aspect of the present invention, a first of the brake members is selectively engageable to connect a member of one of the planetary gearsets with a stationary transmission housing.
In a still further aspect of the present invention, the second of the brake members is selectively engageable to connect a member of one of the planetary gearsets or one of the interconnecting members with the stationary transmission housing.
In yet still a further aspect of the present invention, the first and second of the clutch members are individually selectively engageable to connect at least one member of one of the planetary gearsets with either the input shaft, the output shaft, or another member of one of the planetary gearsets.
In a further aspect of the present invention, the third of the clutch members is selectively engageable to connect a member of one of the planetary gearsets with a member of another of the planetary gearsets.
In another aspect of the present invention, the selectively engageable torque-transmitting mechanisms are engaged in combinations of two to establish at least six forward speed ratios and one reverse speed ratio in the planetary gearsets between the input shaft and the output shaft.